Latent image development apparatus

ABSTRACT

Imaging apparatus including a first member having a first surface having formed thereon a latent electrostatic image, the latent electrostatic image including image regions at a first voltage and background regions at a second voltage, a second member charged to a third voltage intermediate the first and second voltages and having a second surface adapted for resilient engagement with the first surface and a third member adapted for resilient contact with the second surface in a transfer region. The imaging apparatus also includes apparatus for supplying liquid toner to the transfer region thereby forming on the second surface a thin layer of liquid toner containing a relatively high concentration of charged toner particles and apparatus for developing the latent image by the selective transfer of portions of the layer of liquid toner from the second surface to the first surface.

This application is a continuation-in-part of application Ser. No.07/727,599 filed Jul. 9, 1991, now abandoned.

FIELD OF THE INVENTION

The present invention relates generally to development apparatus andmore particularly to latent image development apparatus inelectrophotographic imaging systems.

BACKGROUND OF THE INVENTION

The method of developing a latent image formed on a photoconductivesurface by means of electrophoretic transfer of liquid toner is wellknown in the art. In this method, charged particles suspended in anon-polar insulating carrier liquid migrate under the influence of anelectrostatic field and concentrate in image forming configuration uponrelatively charged or discharged areas of a photoconductive surface. Thelatent image so developed is then transferred to a substrate, such aspaper, either directly or by means of one or more intermediate transfermembers.

In U.S. Pat. No. 4,504,138 a different method for the developing of alatent image is described. The method described involves applying a thinviscous high density layer of toner particles on the circumferentialsurface of a roller and bringing the layer so formed to thephotoconductive surface. Transfer of selected portions of the tonerlayer onto the photoconductive surface then occurs as a function of theelectric field strength of the latent image.

In Canadian Patent 990589, a method of developing electrostatic imagesis described which involves producing a film of liquid toner on a firstapplicator and bringing the applicator in contact with the finalsubstrate which carries a latent image, thereby to develop the image. Asecond applicator bearing a layer of carrier liquid is then brought intocontact with the substrate to remove background deposits and to squeegeeout excess liquid. The film of liquid toner described in Canadian Patent990589 has between 2-4 per cent of toner concentrate dispersed withinthe carrier liquid.

SUMMARY OF THE INVENTION

It is the object of the present invention to provide simplifiedapparatus for the development of latent images in electrophotographicimaging systems by the direct transfer of concentrated liquid toner.There is therefore provided imaging apparatus including:

a first member having a first surface having formed thereon a latentelectrostatic image, the latent electrostatic image including imageregions at a first voltage and background regions at a second voltage;

a second member charged to a third voltage intermediate the first andsecond voltages and having a second surface adapted for resilientengagement with the first surface at a first, transfer, region;

a third member resiliently urged against the second surface at a secondregion;

means for supplying liquid toner comprising charged toner particles andcarrier liquid to the second region, thereby forming on the secondsurface a thin layer of liquid toner containing a relatively highconcentration of charged toner particles;

means for developing the latent image by the selective transfer ofportions of the layer of liquid toner from the second surface to thefirst surface at the first region to form a developed image on the firstmember; and

means for transferring the developed image from the first member to afinal substrate.

There is further provided in a preferred embodiment of the inventionimaging apparatus including:

a first member including a first surface having formed thereon a latentelectrostatic image, the latent electrostatic image having image regionsat a first voltage and background regions at a second voltage;

a second member charged to a third voltage intermediate the first andsecond voltages and having a second surface adapted for resilientengagement with the first surface;

a third member adapted for depositing on the surface of the secondmember a thin layer of liquid toner containing a relatively highconcentration of charged toner particles;

means for obtaining a desired image by selectively transferring portionsof the layer of liquid toner from the surface of the second member tothe photoconductive surface of the first member, the portions remainingon the surface of the second member constituting the desired image; and

means for transferring the desired image to a final substrate.

Either or both of the first and second surfaces are preferably formed ofresilient material.

In one preferred embodiment of the invention the third member is aroller with an elastomer surface, in another it is a resilient blade. Ina third preferred embodiment the third member is a spring-mountedwire-wrapped solid rod. Alternatively the third member is an extrusioncoating head.

Alternatively, in a preferred embodiment of the invention, the thirdmember includes a metallic-screen hollow drum containing liquid tonerand a squeegee blade urged against the inner surface of themetallic-screen, preferably also including a doctor blade in engagementwith the second surface. Preferably the metallic-screen hollow drum,containing liquid toner, and a squeegee blade form a single disposableunit.

Preferably the third member is an integral component of the apparatusfor supplying liquid toner.

In a preferred embodiment of the invention, the liquid toner supplied tothe first transfer region includes toner particles at a concentrationcomparable to that of the thin layer.

In a preferred embodiment of the invention the thickness of the thinlayer is between 5 and 15 micrometers.

In an especially preferred embodiment of the invention the layer ofliquid toner is crumbly in texture and almost dry to the touch.Generally such a layer has a solids concentration of more than 50percent and a thickness of between 2 and 8 micrometers.

There is further provided, in a preferred embodiment of the invention,imaging apparatus including:

a first member including a first surface having formed thereon a latentelectrostatic image, the latent electrostatic image having image regionsat a first voltage and background regions at a second voltage;

a second member having a second surface and being charged to a thirdvoltage intermediate the first and second voltages;

means for resiliently urging the second surface against the firstsurface at an interface region;

means for supplying to the interface region liquid toner comprising ahigh concentration of charged toner particles in a carrier liquid,whereby the latent image is developed as the liquid toner is extrudedbetween the first and second members; and

means for transferring the developed toner image from the first surfaceto a final substrate.

There is further provided, in a preferred embodiment of the invention, aliquid toner developer cartridge, comprising:

a housing;

a quantity of liquid toner concentrate within the housing, the liquidtoner concentrate having a first concentration of solids to liquid; and

means for dispensing a thin layer of liquid toner concentrate from thehousing, whereby the thin layer has a second concentration of solids toliquid which is greater than the first concentration.

The first concentration is preferably at a concentration of greater than25 percent and the second concentration is crumbly in texture and almostdry to the touch and has a solids concentration of greater than 40percent, desirably more than 50 percent.

In a preferred embodiment of the invention, the means for dispensingincludes at least two rollers, the first roller having a resilientsurface and the second roller having a solid surface. Preferably the tworollers are electrified to different electrical potentials.

Preferably, the cartridge includes means for preventing dilution of thequantity of liquid toner concentrate remaining in the housing after thethin layer of toner concentrate has been dispensed therefrom, preferablyincluding capillary means for drawing off excess liquid and a reservoircontaining absorbent material for storing the excess liquid.

In a preferred embodiment of the invention, a portion of the dispensedlayer is not removed from the cartridge and the cartridge includes meansfor reclaiming and dispersing the unremoved portion.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully fromthe following detailed description, taken in conjunction with thedrawings in which:

FIG. 1 is a schematic diagram of imaging apparatus constructed andoperated in accordance with a preferred embodiment of the presentinvention;

FIG. 2 is a schematic diagram of a multi-color imaging apparatus inaccordance with a preferred embodiment of the present invention;

FIG. 3A is a more detailed schematic diagram of a developer assemblyconstructed and operated in accordance with a preferred embodiment ofthe present invention;

FIGS. 3B, 3C, 3D, 3E, 3F, 3G and 3H are schematic diagrams ofalternative embodiments of developer assemblies constructed and operatedaccording to the present invention;

FIG. 4 is a schematic diagram of an additional preferred embodiment ofthe present invention;

FIG. 5 is a schematic diagram of an further preferred embodiment of thepresent invention;

FIG. 6 is a schematic diagram showing toner supply apparatus inaccordance with an alternative embodiment of the present invention; and

FIGS. 7A and 7B hare schematic diagrams of an alternative embodiment ofa developer assembly constructed and operated according to the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to FIG. 1 which illustrates imaging apparatusconstructed and operative in accordance with a preferred embodiment ofthe present invention.

The apparatus of FIG. 1 comprises a drum 10 arranged for rotation in adirection generally indicated by arrow 14. Drum 10 preferably has acylindrical photoconductive surface 16 made of selenium, a seleniumcompound, an organic photoconductor or any other suitable photoconductorknown in the art.

When the apparatus is operated, drum 10 rotates and photoconductivesurface 16 is charged by a charger 18 to a generally uniformlypre-determined voltage, typically on the order of 1000 volts. Charger 18may be any type of charger known in the art, such as a corotron, ascorotron or a roller.

Continued rotation of drum 10 brings charged photoconductive surface 16into image receiving relationship with an exposure means such as a lightsource 19, which may be a laser scanner (in the case of a printer) orthe projection of an original (in the case of a photocopier). Lightsource 19 forms a desired latent image on charged photoconductivesurface 16 by selectively discharging a portion of the photoconductivesurface, the image portions being at a first voltage and the backgroundportions at a second voltage. The discharged portions preferably have avoltage of less than about 100 volts.

Continued rotation of drum 10 brings charged photoconductive surface 16,bearing the electrostatic latent image, into operative engagement withthe surface 21 of a developer roller 22 which is part of developerassembly 23, more fully described below with reference to FIGS. 3Athrough 3H. Developer roller 22 rotates in a direction opposite that ofdrum 10, as shown by arrow 13, such that there is substantially zerorelative motion between their respective surfaces at the point ofcontact. Surface 21 of developer roller 22 is preferably composed of asoft polyurethane material, preferably made more electrically conductiveby the inclusion of conducting additives, while developer roller 22 maybe composed of any suitable electrically conductive material.Alternatively, drum 10 may be formed of a relatively resilient material,and in such case surface 21 of developer roller 22 may be composed ofeither a rigid or a compliant material.

As described below, surface 21 is coated with a very thin layer ofconcentrated paste of liquid toner, preferably containing 15-35% chargedtoner particles, desirably more than 25% solids. The layer is preferablybetween 5 and 30 μm, more preferably between 5 and 15 μm, thick.Developer roller 22 itself is charged to a voltage that is intermediatethe voltage of the charged and discharged areas on photoconductivesurface 16.

In a preferred embodiment of the invention, a concentrated form ofliquid toner such as the toner described in Example 1 of U.S. Pat. No.4,794,651, the disclosure of which is incorporated herein by reference,is used although other types of toner are usable in the invention. Forcolored toners the carbon black in the preferred toner is replaced bycolored pigments as is well known in the art.

When surface 21 of developer roller 22 bearing the layer of liquid tonerconcentrate is engaged with photoconductive surface 16 of drum 10, thedifference in voltages between developer roller 22 and photoconductivesurface 16 causes the selective transfer of the layer of toner particlesto photoconductive surface 16, thereby developing the desired latentimage. Depending on the choice of toner charge polarity and the use of a"write-white" or "write-black" system, the layer of toner particles willbe selectively attracted to either the charged or discharged areas ofphotoconductive surface 16, and the remaining portions of the tonerlayer will continue to adhere to surface 21 of developer roller 22.

Because the transfer of the concentrated layer of toner is much lessmobility dependent than in normal electrophoretic development, theprocess described above occurs at a relatively high speed. Also, sincethe layer already has a high density and viscosity, there is no need toprovide for metering devices, rigidizing rollers and the like whichwould otherwise be necessary to remove excess liquid from the developedimage to attain the desired density of toner particles of the developedimage.

For multicolor systems, as shown in FIG. 2, a plurality of developerrollers may be provided, one for each color, which are sequentiallyengaged with photoconductive surface 16 to develop sequentially producedlatent images.

The latent image developed by means of the process described above isthen directly transferred to a desired substrate in a manner well knownin the art. Alternatively, as shown in FIG. 1, there may be provided anintermediate transfer member 40, which may be a drum or belt and whichis in operative engagement with photoconductive surface 16 of drum 10bearing the developed image. Intermediate transfer member 40 rotates ina direction opposite to that of photoconductive surface 16, as shown byarrow 43, providing substantially zero relative motion between theirrespective surfaces at the point of image transfer. Intermediatetransfer member 40 is operative for receiving the toner image fromphotoconductive surface 16 and for transferring the toner image to afinal substrate 42, such as paper. Disposed internally of intermediatetransfer member 40 there may be provided a heater 45, to heatintermediate transfer member 40 as is known in the art. Transfer of theimage to intermediate transfer member 40 is preferably aided byproviding electrification of intermediate transfer member 40 to providean electric field between intermediate transfer member 40 and the imageareas of photoconductive surface 16. Intermediate transfer member 40preferably has a conducting layer 44 underlying an elastomer layer 46,which is preferably a slightly conductive resilient polymeric layer.

Various types of intermediate transfer members are known and aredescribed, for example in U.S. Pat. No. 4,684,238, PCT Publication WO90/04216 and U.S. Pat. No. 4,974,027, the disclosures of all of whichare incorporated herein by reference.

Following the transfer of the toner image to substrate 42 or tointermediate transfer member 40, photoconductive surface 16 engages acleaning station 49, which may be any conventional cleaning station.Scraper 56 completes the removal of any residual toner which may nothave been removed by cleaning station 49. A lamp 58 then completes thecycle by removing any residual charge, characteristic of the previousimage, from photoconductive surface 16.

It is to be understood that, in a preferred embodiment of the invention,the liquid toner concentrate which is transferred to drum 10 hassubstantially the same toner particle concentration as the image when itis transferred from drum 10. This is in contrast to traditional liquiddevelopment where the liquid developer has a comparatively lowconcentration of particles before development and where excess liquid isremoved from the image before transfer from the photoconductor. It isalso in contrast to U.S. Pat. No. 4,504,138, in which the toner suppliedto the drum (and which is transferred to the drum) is more concentrated,but where excess liquid must still be removed from the image beforetransfer to the final substrate. In a preferred embodiment of thepresent invention, the starting toning material is at a solidsconcentration substantially equal to that of the image transferred fromthe drum. The toning material may be further concentrated before contactwith drum 10 or mechanical squeegeeing may be used to further increasethe concentration during the process of transfer of toner to the drum.

Reference is now made to FIG. 3A which shows the construction andoperation of a preferred developer assembly 23A. Developer assembly 23Acomprises a toner dispenser 62 which dispenses liquid toner concentrateonto the surface of a roller 64 arranged for rotation in a directionindicated by arrow 68. Roller 64 is preferably formed of metal androller 21 is formed of a metal core having a covering of an elastomermaterial, which is preferably a slightly conductive resilient polymericmaterial, as described for example, in U.S. Pat. No. 3,959,574 or U.S.Pat. No. 3,863,603. Roller 64 may have a very thin coating of polymermaterial. As it rotates, roller 64 is resiliently urged against surface21 of developer roller 22, by virtue of a spring 70, and a thin layer ofliquid toner concentrate is formed on surface 21 of developer roller 22.The thickness of the layer is a function of the pressure applied and thehardness of the surfaces.

Roller 64 may also be electrified by a D.C. source to avoid depositionof toner concentrate on roller 64. It may further or alternatively beconnected to an AC source, which is operative to reduce somewhat theviscosity of the toner concentrate and generally to cause the depositionof a smoother layer on surface 21 of developer roller 22.

In a preferred embodiment of the invention, the liquid toner is suppliedat a pre-determined concentration, equal to the concentration of tonerparticles necessary for the desired optical density of the final image.Supply of the liquid toner concentrate at the pre-determinedconcentration obviates the need for pumps, tanks, sensors and othercostly apparatus which would otherwise be needed in the event a dilutesolution of liquid concentrate is provided.

In an alternative embodiment, the liquid toner is supplied at aconcentration less than that required for optimal development of thelatent image. In such event, roller 64 may also function as a mechanicaland electrical "squeegee" roller, i.e. when urged against surface 21 ofdeveloper roller 22, it mechanically removes excess toner fluid from thelayer impressed on surface 21, and when charged with a suitable electricpotential, it repels the charged toner particles and causes them to moreclosely adhere to surface 21. The excess fluid which has been removed isrecovered for reuse. Applicants have found that the solids content ofthe layer is mainly a function of the mechanical properties of therollers and of the applied voltages and pressures and is only slightlyinfluenced by the initial concentration for a considerable range ofinitial toner concentrations.

As described above, the layer of liquid toner which is deposited bymeans of roller 64 on surface 21 is selectively transferred tophotoconductive surface 16 in the process of developing the latentimage. In principle, the system described above does not require thatthe portions of the toner layer that have not been used in thedevelopment of the latent image be removed from developer roller 22between cycles. However, in the event the toner is of a type whichbecomes discharged by the electric fields in the interface between thesurfaces of developer roller 22 and drum 10, a cleaning station 72 maybe provided, which may comprise a brush or comb or similar apparatus, toremove the excess toner concentrate from surface 21 of developer roller22. The toner so removed may then be pumped back for reuse after mixturewith fresh toner, or may be mixed with the toner being fed into the nipbetween developer roller 22 and roller 64.

Reference is now made to FIGS. 3B through, 3H, which show alternateembodiments 23B through 23H, of developer assembly 23 in accordance withthe invention. FIGS. 3B through 3H are identical to FIG. 3A, except thatin each case roller 64 has been replaced by a different structurecapable of supplying a thin layer of viscous toner concentrate ondeveloper roller 22.

In FIG. 3B, roller 64 is replaced by a resilient blade 74, which may becomposed of the same material as roller 64 and which is preferablyelectrically biased to cause better adhesion of the toner particles tosurface 21 and better release from blade 74.

In FIG. 3C, roller 64 is replaced by a spring-mounted wire-wrapped solidrod 65, and the coating of surface 21 is accomplished by a "wire-rod"process as is well known in the art. Rod 65 may also be electricallybiased.

In FIG. 3D, roller 64 is replaced by a metallic-screen drum 74 in whicha squeegee blade 75 is mounted and which is urged against the innersurface of the metallic screen 74 near its point of contact withdeveloper roller 22. Liquid toner concentrate is supplied to the insideof drum 74 and is deposited on surface 21 through the screen when drum74 is rotated together with roller 22. In a preferred embodiment, themetallic-screen drum together with the squeegee blade and a supply ofliquid toner concentrate are supplied as a disposable unit which isreplaced when the toner material is depleted.

FIG. 3E shows a preferred alternative to the disposable unit described.In the embodiment shown in FIG. 3E, toner concentrate is fed tometallic-screen drum 74 from a reservoir 80 by pump 82 via conduit 84.The pressure of the toner concentrate in drum 74 is kept substantiallyconstant by pump 82. This pressure is not sufficient to force the tonerconcentrate through the screen over most of its surface. However duringrotation of drum 74 the tip of squeegee blade 75 increases the pressuresufficiently to force the concentrate through the holes to coat roller22.

Alternatively, as shown in FIG. 3F, a replaceable pressurized container86 of toner concentrate replaces reservoir 80 and pump 82. In theembodiments of FIG. 3E and 3F, drum 74 is preferably not removed whenthe toner is replenished.

In FIG. 3G, roller 64 is replaced by an extrusion coating head 76, whichdispenses the liquid toner concentrate in a layer upon surface 21 ofdeveloper roller 22.

FIG. 3H shows an alternative embodiment of the developer assembly inaccordance with the invention. The apparatus of FIG. 3H is similar tothat of FIG. 3A, except that the liquid toner concentrate is supplied tothe interface between the surface of roller 64 and a doctor blade 77. Athin layer of the toner concentrate is formed on the surface of roller64 which is then transferred in the manner described above.

Reference is made to FIG. 4 which shows a cross-sectional schematic viewof an alternative embodiment of the invention in which concentratedliquid toner is supplied to an interface between a squeegee roller 120and drum 10 bearing a latent image. As in the previous embodimentsroller 120 and drum 10 are mechanically resiliently urged together. Theembodiment of FIG. 4 differs from the other embodiments in that a thinlayer of concentrated material is formed by extrusion between thesqueegee roller and the drum as they roll together and are urged againsteach other. As seen in FIG. 4 the thin layer immediately separates intoimage portions which remain on drum 10, and background portions whichremain on roller 120.

Reference is now made to FIG. 5 which shows another embodiment of theapparatus in accordance with the invention. The apparatus of FIG. 5 issimilar to that of FIG. 1 except that the apparatus is used for a"reversal" development on roller 22 by the latent image onphotoconductive surface 16. In this embodiment, the desired image isformed by the areas of toner concentrate which remain on the surface ofdeveloper roller 22 after the development of photoconductive surface 16,and it is developer roller 22 and not drum 10 which is then brought intooperative association with an intermediate transfer member (not shown)or a final substrate so as to obtain a print of the desired image. Alsoshown in FIG. 5 is a pump 76 which is operative to pump back for reusethe toner concentrate which has been removed from photoconductivesurface 16 by cleaning station 56 at the conclusion of the imagingcycle. Any of the developer assemblies described above may also be usedin the context of this embodiment.

Reference is now made to FIG. 6, which shows an alternative embodimentof a toner supply apparatus in accordance with the invention. Theapparatus of FIG. 6 comprises a housing 100 to which arms 108 and 110are attached. Arms 108 and 110 are adapted to be resiliently urgedagainst surface 21 of developer roller 22. Interior to housing 100 is apiston-like platform 112 which is spring-mounted on the base of housing100. In operation, housing 100 is filled with liquid toner concentratewhich is pushed in the direction of developer roller 22 by the action ofa spring 113 on platform 112. Arms 108 and 110 serve to contain theliquid toner concentrate from spilling outward, and arm 110 furtherfunctions as a blade to meter the deposition of the required amount ofliquid toner on surface 21 of developer roller 22. Arm 110 may also bebiased electrically as explained above.

Alternatively, spring 113 may be replaced by a gas-pressure apparatuswhich is operative to cause dispensing of the liquid toner concentrateby propelling platform 112 in the direction of developer roller 22.

In another embodiment of the invention, housing 100 together with asupply of liquid toner concentrate and roller 22 may be supplied as adisposable unit, being replaced when the supply of liquid tonerconcentrate is depleted.

Reference is now made to FIGS. 7A and 7B which show an alternativeembodiment of developer assembly 23 in accordance with a preferredembodiment of the invention. In this embodiment, the developer assembly(including the developer roller and associated elements) is not a fixedcomponent within the imaging apparatus itself, but rather takes the formof a replaceable cartridge 150 which can be readily inserted into thecasing of the imaging apparatus (not shown) and removed therefrom whenthe supply of liquid toner concentrate has been depleted. As shown ingreater detail in FIG. 7B, cartridge 150 comprises a housing 152 and aninternal space 154 containing a supply of liquid toner concentrate. Inaccordance with a preferred embodiment of the invention, the liquidtoner supplied with cartridge 150 contains a relatively highconcentration of charged toner particles, on the order of 30%, andcarrier liquid. A movable platform 156 is mounted internally to the baseof housing 152 by a spring 158, which is at its maximum tension whenspace 154 is initially filled to its capacity with liquid tonerconcentrate. The area 160 between housing 152 and movable platform 156may be packed with any suitable liquid-absorbing material, such as asponge. Platform 156 contains a network of tiny capillaries 162 throughwhich excess liquid in space 154 may drip into space 160 and be absorbedby the sponge-like material contained therein.

Mounted within housing 152 is a roller 170 which is composed of anysuitable electrically conducting material and which has a surfacecomposed of a soft polyurethane material, preferably made moreelectrically conductive by the inclusion of conducting additives. In apreferred embodiment of the invention roller 170 has a small diameter,desirably less than about 4 cm and preferably about 2.25 cm. The surfaceof roller 170 protrudes somewhat from the opening of housing 152, suchthat when cartridge 150 is installed in the imaging apparatus, thesurface of roller 170 contacts the photoconductive surface of drum 10.When the apparatus is activated, roller 170 is electrically charged andis caused to rotate in the direction indicated by arrow 171. As is morefully described below, a layer of highly concentrated liquid toner isdeposited on the surface of roller 170 which then functions as adeveloper roller with regard to latent images formed on thephotoconductive surface of drum 10, in a manner similar to thatdescribed above with regard to other embodiments of the invention.

In addition to roller 170, cartridge 150 comprises two other rollers,172 and 174, which are mounted within housing 152 such that the surfaceof roller 172 contacts the surface of roller 170 at point 182 and thesurface of roller 174 contacts the surface of roller 172 at point 184.Rollers 172 and 174 are composed of any suitable electrically conductingmaterial. Roller 172 has a diameter which is significantly smaller thanthat of roller 170. Thus, if roller 170 has a diameter of 2.25 cm.,roller 172 has a diameter of 1.5 cm.

When cartridge 150 is installed and the imaging apparatus is inoperation, rollers 172 and 174 are electrically charged and are causedto rotate in a direction opposite that of roller 170 (as indicated byarrows 173 and 175), while they are urged against the resilient surfaceof roller 170.

It is a feature of this embodiment of the invention that the layerdeposited on roller 170 has a very high solids concentration ofpreferably greater than about 40 percent and typically between 50 and 60per cent, when the initial concentration of solids in space 154 ispreferably above 25% and typically about 30 per cent. This layer oftoner has been found to be almost dry to the touch, non-flowing andcrumbly in texture. It has also been found that the quality of thedeveloped latent image is enhanced greatly as a result, and noadditional drying mechanism is needed when the image is transferred tothe final substrate. Since so much liquid has been removed from thelayer a thickness of 2-8 micrometers on roller 170 is sufficient.

Because of the relatively small diameters of rollers 170 and 172, arelatively small force of up to 300 gm-force/cm of length applied at theline of contact of rollers 170 and 172 is sufficient. For this force, ifnegatively charged toner particles are used, roller 170 preferably ischarged to an electrical potential which is 150 volts more positive thanthat of roller 172 and roller 174 is charged to an electrical potentialwhich is 250 volts more positive than roller 170.

It will readily be seen that since interior space 154 of housing 152 isfilled with liquid toner concentrate, when the apparatus is activatedand rollers 170 and 172 rotate, the interaction between roller 170 and172 at contact point 182 results in the deposition of a concentratedlayer of liquid toner on the surface of roller 170. Then, as roller 170continues to rotate, it functions in turn as a developer roller withregard to the latent-image-bearing surface of drum 10, with portions ofthe layer of the dry to the touch liquid toner concentrate beingselectively transferred to the surface of drum 10, thereby developingthe latent image, as explained above with regard to the otherembodiments of the invention. As described above, because of thesqueegee action of the resilient surface of roller 170 at contact point182, a large proportion of the carrier liquid contained within the tonerconcentrate is squeezed out as the layer of toner is deposited on roller170.

After portions of the layer of toner concentrate have been transferredto the surface of drum 10 to develop the latent image, the remainingportions of the toner layer on roller 170 continue to rotate on thesurface of roller 170 until they reach contact point 184 between roller170 and roller 174. Then, because of the relative electrical potentialson roller 170 and roller 174, the remaining portions of the toner layerare transferred to roller 174 at contact point 184. Downstream ofcontact point 184, a resilient blade 176 which is anchored to theinternal wall of housing 152, scrapes off the remaining portions of thetoner layer from the surface of roller 174.

Because the portions of toner concentrate which are scraped off ofroller 174 are dry and crumbly, they will not disperse easily within theliquid toner concentrate remaining in the cartridge. To aid in thedispersion process, a pair of oppositely turning teeth-bearing rods 178and 180 are mounted within housing 152, such that the portions of drytoner scraped off of roller 174 fall between them and are broken apartby the interaction of the teeth on the rods. The turbulence caused bythe rotational movement of rods 178 and 180 also aid in the dispersionof the drier portions of the toner within the solution of tonerconcentrate.

As the initial supply of toner concentrate contained within space 154 isgradually depleted in the process of developing the latent image, theaction of spring 158 causes platform 156 to push the mass of tonerconcentrate within space 154 in the direction of contact point 182,until space 154 is virtually emptied of toner concentrate. A seal 190 isalso provided between housing 152 and roller 172, so as to ensure thatliquid toner may not be released from cartridge 150 except as a resultof the interaction of roller 170 and roller 172 at contact point 182.

As a consequence of the fact that a large proportion of the carrierliquid contained within the toner concentrate is squeegeed out when thelayer of toner is deposited on roller 170, the concentrate stillremaining within space 154 is subject to an ongoing process of dilution,as the concentrate is used up. Were this dilution process allowed tocontinue unchecked, it could result in an unevenness in the liquidcontent of the toner layers being deposited on roller 170 as the supplyof concentrate was being depleted. It is for this reason that the area160 between housing 152 and movable platform 156 is packed with asponge-like material and platform 156 is fitted with a network of tinycapillaries 162. Excess carrier liquid in the toner concentrategenerated by the squeegee action of rollers 170 and 172 will drainthrough these capillaries and be absorbed by the sponge-like material,so that at any given time during the life-span of the cartridge, theliquid content of the toner concentrate will remain substantially thesame.

The developer assembly described with reference to FIGS. 7A and 7B maybe easily adapted for use with the embodiments of FIGS. 1, 2, 4 and 5.

Although a variety of toners are suitable, a preferred toner for theembodiments of FIGS. 7A and 7B is made in the following method:

Compounding

36 grams of Picotoner 1278 (Hercules), a styrene acrylate copolymer, isloaded on a Brabender two-roll mill preheated to 160° C. 30 grams ofMogul-L (Cabot) carbon black are added in small amounts during a periodof about 10 minutes while working of the material is continued. 84 gramsof Iotec 8030 (EXXON), an acrylic acid ethylene copolymer partial sodiumsalt, is added during 10 additional minutes of compounding. The materialis discharged and after it is cooled to room temperature it is shreddedin a granulator and then cryogenically ground in a Retsch centrifugalmill. The resulting material is used in the size reduction step.

Size Reduction

570 grams of powdered material produced by the compounding step isloaded, together with 1330 grams of Norpar-13 (EXXON) in a Union Processsize 1S attritor filled with 3/16" carbon steel balls. The material isground at 20° C. and 200 RPM for 16 hours to a median diameter of 2.6microns as measured by a Shimadzu particle size analyzer. The resultingmaterial is screened through a 300 micrometer sieve to remove largeparticles.

The resulting toner concentrate is charged with charge director as isknown in the art. A variety of charge directors known in the art areoperative in this embodiment of the invention. A preferred chargedirector is Lubrizol 890 (Lubrizol Corporation).

Alternatively, the carrier liquid is at least partially replaced by agrease or petrolatum. This material has a high viscosity and isthixotropic, thereby reducing leaks.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present invention isdefined only by the claims that follow:

What is claimed is:
 1. Imaging apparatus comprising:a first memberhaving a first surface having formed thereon a latent electrostaticimage, the latent electrostatic image including image regions at a firstvoltage and background regions at a second voltage: a second membercharged to a third voltage intermediate the first and second voltagesand having a second surface adapted for operative engagement with thefirst surface at a first, development, region; a third memberresiliently urged against the second surface at a second region; aliquid toner supply system which supplies liquid toner comprisingcharged toner particles and carrier liquid to the second region andforms a thin layer of liquid toner containing a concentration of chargedtoner particles greater than 15% on the second surface; means fordeveloping the latent image by the selective transfer of portions of thelayer of liquid toner from the second surface to the first surface atthe first region to form a developed image on the first member; andmeans for transferring the developed image from the first member to afinal substrate.
 2. Imaging apparatus according to claim 1 wherein theliquid toner supplied to the second region comprises less than 35%charged toner particles.
 3. Imaging apparatus according to claim 2wherein the concentration of toner particles in the liquid tonersupplied to the second region is substantially the same as in the thinlayer of liquid toner.
 4. Imaging apparatus according to claim 1 whereinthe concentration of toner particles in the liquid toner supplied to thesecond region is substantially the same as in the thin layer of liquidtoner.
 5. Imaging apparatus according to claim 1 wherein theconcentration of toner particles in the liquid toner supplied to thesecond region is substantially less than in the thin layer of liquidtoner.
 6. Imaging apparatus according to claim 1 wherein the thin layerof liquid toner comprises more than 20% charged toner particles. 7.Imaging apparatus according claim 1 wherein the layer liquid toner iscrumbly in texture and almost dry to the touch.
 8. Imaging apparatusaccording to claim 1 wherein the thin layer of liquid toner has aconcentration of toner particles greater than 40 per cent.
 9. Imagingapparatus according to claim 8 wherein the thin layer of liquid tonerhas a concentration of toner particles greater than 50 per cent. 10.Imaging apparatus according to claim 1 wherein the layer of liquid tonercomprises less than 35% charged toner particles.
 11. Imaging apparatusaccording to claim 1 wherein the layer of liquid toner has a thicknessbetween 2 and 8 micrometers.
 12. Imaging apparatus according to claim 1wherein the thin layer has a thickness between 5 and 15 micrometers. 13.Imaging apparatus according to claim 1 wherein at least one of the firstand second surfaces is formed of a resilient material.
 14. Imagingapparatus according to claim 1 wherein the third member is a roller withan elastomer surface.
 15. Imaging apparatus according to claim 1 whereinthe third member is a resilient blade.
 16. Imaging apparatus accordingto claim 1 wherein the third member is a spring-mounted wire-wrappedsolid rod.
 17. Imaging apparatus according to claim 1 wherein the thirdmember comprises a metallic-screen hollow drum containing liquid tonerand a squeegee blade urged against the inner surface of themetallic-screen.
 18. Imaging apparatus according to claim 17 wherein themetallic-screen hollow drum containing liquid toner and a squeegee bladeform a single disposable unit.
 19. Imaging apparatus according to claim1 including a doctor blade in engagement with the second surface. 20.Imaging apparatus according to claim 1 wherein the third member is anintegral component of the means for supplying liquid toner.
 21. Imagingapparatus according to claim wherein the third member end the means forsupplying liquid toner form a single disposable unit.
 22. Imagingapparatus comprising:a first member including a first surface havingformed thereon a latent electrostatic image, the latent electrostaticimage having image regions at a first voltage and background regions ata second voltage; a second member charged to a third voltageintermediate the first and second voltages and having a second surfaceadapted for resilient engagement with the first surface; a third memberadapted for depositing on the surface of the second member a thin layerof liquid toner containing a concentration of charged Toner particlesgreater than 15%; means for obtaining a desired image by selectivelytransferring portions of the layer of liquid toner from the surface ofthe second member to the photoconductive surface of the first member,the portions remaining on the surface of the second member constitutingthe desired image; end means for transferring the desired imager to afinal substrate.
 23. Imaging apparatus comprising:a first memberincluding a first surface having formed thereon a latent electrostaticimage, the latent electrostatic image having image regions at afirst-voltage and background regions at a second voltage; a secondmember having a second surface and charged to a third voltageintermediate the first and second voltages; means for resiliently urgingthe second surface against the first surface at an interface region; asupply system which supplies a viscous liquid toner comprising a highconcentration of charged toner particles in a carrier liquid greaterthan 15% to the interface region; means for extruding the viscous liquidconcentrate between the first and second members thereby to develop theelectrostatic image; and means for transferring the developed tonerimage from the first surface to a final substrate.
 24. A liquid tonerdeveloper cartridge comprising:a housing; a quantity of liquid tonerconcentrate within the housing, the liquid toner concentrate having afirst concentration of solids to liquid; and a dispensing mechanismwhich dispenses liquid toner concentrate from the housing having asecond concentration of solids to liquid which is greater than the firstconcentration.
 25. A liquid toner developer cartridge according to claim24 wherein the first concentration is greater than 30 percent and thesecond concentration is greater than 50 percent.
 26. A liquid tonerdeveloper cartridge according to claim 24 or claim 25 wherein the firstconcentration is less than 35 percent and the second concentration isgreater than 50 percent.
 27. A liquid toner developer cartridgeaccording to claim 24 wherein the dispensed liquid toner concentrate iscrumbly in texture end almost dry to the touch.
 28. A liquid tonerdeveloper cartridge according to claim 27 and including a charger whichelectrifies the two rollers to different electrical potentials.
 29. Aliquid toner developer cartridge according to claim 24 wherein thedispensing mechanism includes at least two rollers, the first rollerhaving a resilient surface and the second roller having a solid surface.30. A liquid toner developer cartridge according to claim 24 andincluding a concentrator which reduces dilution of the quantity ofliquid toner concentrate remaining in the housing after liquid tonerconcentrate has been dispensed therefrom.
 31. A liquid toner developercartridge according to claim 30 wherein a portion of the dispensedconcentrate is not removed from the cartridge and wherein the unremovedportion is reclaimed.
 32. A liquid toner developer cartridge accordingto claim 30 wherein the means for reducing dilution comprises acapillary which draws off excess liquid and a reservoir containingabsorbent material which stores the excess liquid.
 33. A liquid tonerdeveloper cartridge according to claim 32 and further including adisperser which disperses the reclaimed portion.
 34. A liquid tonerdeveloper cartridge according to claim 33 wherein the disperser a pairof rods bearing teeth which rotate in opposite directions.
 35. A liquidtoner developer cartridge according to claim 24 and also comprising adeveloper roller on which the liquid toner concentrate is dispensed. 36.Imaging apparatus comprising:a first member having a first surfacehaving formed thereon a latent electrostatic image, the latentelectrostatic image including image regions at a first voltage andbackground regions at a second voltage; a cartridge comprising:ahousing; a quantity of liquid toner concentrate within the housing, theliquid toner concentrate comprising toner particles and carrier liquidend having a first concentration of solid to liquid; and a dispensingmechanism which dispenses liquid toner concentrate from the housinghaving a second concentration of solids to liquid which is greater thanthe first concentration, said liquid toner concentrate being dispensedon a second surface of a second member, said second member being chargedto a third voltage intermediate the first and second voltages and saidsecond surface being adapted for operative engagement with the firstsurface eta first, development, region whereat the latent images isdeveloped by the selective transfer of portions of the layer of liquidtoner from the second surface to the first surface at the first regionto form a developed image on the first member; end means fortransferring the developed image from the first member to a finalsubstrate.
 37. An imaging method comprising the steps of:forming alatent electrostatic image including image regions at a first voltageand background regions at a second voltage on a first surface of a firstmember; charging a second member having a second surface adapted foroperative engagement with the first surface at a first, development,region to a third voltage intermediate the first and second voltages;resiliently urging a third member against the second surface at a secondregion; supplying liquid toner comprising charged toner particles andcarrier liquid to the second region end forming a thin layer of liquidtoner containing a concentration of charged toner particles greater than15% on the second surface; developing the latent image by the selectivetransfer of portions of the layer of liquid toner from the secondsurface to the first surface at the first region to form a developedimage on the first member; and transferring the developed image from thefirst member to a final substrate.
 38. An imaging method comprising thesteps of:forming a latent electrostatic image including image regions ata first voltage and background regions at a second voltage on a firstsurface of a first member; charging a second surface of a second memberto a third voltage intermediate the first and second voltages;resiliently urging the second surface against the first surface;depositing on the surface of the second member a thin layer of liquidtoner containing a concentration of charged toner particles greater than15%; forming a desired image by selectively transferring portions of thelayer of liquid toner from the surface of the second member to the firstsurface of the first member, the portions remaining on the surface ofthe second member constituting the desired image; and transferring thedesired image to a final substrate.